CAMBRIDGE, Mass., Jan. 23, 2014 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today announced enrollment of its first patient in a Phase 1 dose-escalating clinical study of MM-398 in conjunction with cyclophosphamide for the treatment of pediatric solid tumors. MM-398 is a stable nanoliposomal irinotecan that is designed to exploit leaky tumor vasculature for enhanced drug delivery to tumors. "Our preclinical research suggests that MM-398 accumulates particularly well in Ewing's sarcoma tumors," said Jonathan Fitzgerald, PhD, MM-398 Senior Director at Merrimack. Preclinical research indicates that MM-398 administration results in delivery to the tumor of larger quantities of chemotherapy that are sustained for longer time periods compared with conventional chemotherapy administration. These effects may be applicable across other types of pediatric solid tumors. The most common forms of pediatric solid tumors include Ewing's sarcoma, rhabdomyosarcoma, neuroblastoma, and osteosarcoma. "We are encouraged by the sensitivity of Ewing's sarcoma tumors to MM-398 that has been demonstrated in the laboratory setting. We are hopeful that the clinical results will mirror what we have seen in the preclinical studies," said C Patrick Reynolds, MD, PhD, Director of the Texas Tech University Health Sciences Center School of Medicine Cancer Center and of the South Plains Oncology Consortium. This Phase 1 study will assess the safety of MM-398 in combination with cyclophosphamide in patients with recurrent or refractory pediatric solid tumors and will seek to determine the recommended Phase 2 dose. The trial will be sponsored by the South Plains Oncology Consortium and will be executed by participating institutions. Approximately 40 patients from 1 to 21 years old are expected to be enrolled. The first patient was dosed at the University of Texas Southwestern Medical Center. About Ewing's Sarcoma Ewing's sarcoma is an aggressive bone cancer primarily affecting children and adolescents, and is caused by the activation of the EWS gene due to a translocation between chromosomes 11 and 22. 1 There is currently no known risk factor or prevention for this disease. 2 Treatment includes multidrug chemotherapy and surgical resection, with radiation when necessary. 3 Metastatic Ewing's sarcoma is often seen at the time of diagnosis, and occurs in approximately 25% of patients. 4 While the outlook for patients with localized tumors is encouraging, with a five-year survival rate of approximately 60%-70%, outcomes for patients with metastatic tumors remain poor, with a five-year survival rate of approximately 20-30%. 5 About MM-398 MM-398 is a stable nanoliposomal irinotecan, designed to optimize the delivery of irinotecan by extending the duration of circulation in the body and preferentially activating the drug within the tumor to achieve higher levels of the active cytotoxic, SN-38. MM-398 is being evaluated in several clinical trials including a Phase 3 study in metastatic pancreatic cancer, a Phase 2 study in patients with metastatic colorectal cancer and a Phase 1 cross indication translational study. MM-398 is not approved for any indication by the FDA or any other regulatory agency. Under a 2011 agreement with PharmaEngine, Inc. (Taipei, Taiwan), Merrimack consolidated the worldwide development and commercialization rights to MM-398, with the exception of commercialization rights in Taiwan which are held by PharmaEngine, Inc.